A holding portion includes at least three pressing members which are operable to press an inner peripheral of a hole formed on the medium. The pressing members are movable between first positions where the pressing members do not come in contact with the inner peripheral and second positions where the pressing members come in contact with and press the inner peripheral. Each of the pressing members is adapted to interlockingly move with each other when moving toward the first positions and to press the inner peripheral independently from the other members when positioning the second positions.